CEREBELLUM. 



517 



and white matter, and might be compared with the gyri of the cere- 

 brum, but are smaller and without convolution. These laminse are 

 separated by slightly-curved grooves or sulci of different depths. 



Fissures. — One principal fissure, or sulcus, named the great horizontal 

 fissure (fig. oGO,fh), divides the cerebellum into an upper and a lower 

 portion. It begins in front at the entrance of the middle peduncles, 

 and passes horizontally backwards round the outer border of the 

 hemispheres. From this primary fissure, numerous others proceed on 

 both the upper and under surfaces, forming nearly parallel curves, 

 having their concavities turned forwards, and separating the folia from 

 each other. All these furrows do not go entirely round the hemis- 

 phere, for many of them coalesce one with another ; and some of the 

 smaller furrows have even an oblique course between the others. More- 

 over, on opening the larger fissures, many of the folia are seen to lie 

 concealed within them, and do not reach the surface of the cerebellum. 



Lobes. — Certain fissures, which are deeper than the rest, and constant 

 in their position, have been described as separating the cerebellum into 

 lobes, which are named as follows. 



The central lobe, situated on the upper surface (fig. 360, 9), consists of 

 about eight folia, immediately adjoining the anterior concave border. 

 The snj)erior and anterior lobe, sometimes called quadrate (1. q), and the 

 superior and jwsterior lobe (p. s.), are placed between the central lobe and 

 the great horizontal fissure. On the under surface (fig. 3G2) are seen 



362. 



Fig. 362. — Inferior Surface of the Cekebellum with the Posterior Medullary 

 Velum (Allen Thomsou after Eeil and ReicLert, and from nature). | 



The meduUa oblongata has been in great part removed by a cut passing through it 

 near the pons Varolii ; the two amygdaloid lobules have also been removed, and the 

 medulla and pons Varolii pulled downwards in order to bring into view the posterior 

 medullary velum. 



p s, posterior superior lobe of the cerebellum ; f It, horizontal fissure ; p i, posterior 

 inferior lobe ; g, lobulus gracilis ; b i, biventral lobe ; c, placed on the folia which pass 

 across between the hemispheres of opposite sides ; p, pyramid ; u, uvula ; n, placed in 

 the fourth ventricle immediately below the nodule ; 2^ i', on each side, placed on the cut 

 surface where the amygdalas have been removed, points by a line to the posterior medullary 

 velum ; v, v, cavity of the fourth ventricle within the borders of the velum and behind 

 the inferior cerebellar peduncles ; the cavity extends on each side into the pedicle of the 

 flocculus, /; ni, section of the medulla oblongata, in which the posterior opening of the 

 olivarj' capsules of grey matter is sho-\^Ti ; VI, sixth neiwes ; V, roots of the fifth nerves, 

 and alaove them, the facial and auditory roots. 



